This invention is related to the analysis of flowing streams of liquids, solids or mixed liquids and solids by nuclear magnetic resonance (NMR). In particular, it is an apparatus that is small enough, economical enough and easy enough to operate so that it is useful for making measurements in applications such as the production of foods and the like.
The analysis of materials using NMR requires a region of space containing a magnetic field that is either extremely uniform in magnetic flux density or else extremely uniform in the spatial gradient of magnetic flux density. In such a region, a sample to be analyzed is subjected to a short pulse of electromagnetic energy at a predetermined frequency that is a function of the ions to be analyzed and of their chemical bonding. The pulse is coupled to the sample by a surface coil. A typical pulse duration is of the order of fifty microseconds, although the pulse width that is chosen is a function of the characteristic relaxation time of the material being analyzed. The magnetic field causes the dipole moments of the constituents of the sample to become aligned along lines of magnetic flux. If the field is strong and uniform to a relatively high degree of precision, the dipole moments will be essentially parallel to each other. The electromagnetic energy coupled to the sample changes the alignment of the magnetic dipoles in the sample so as to align them with the net flux, which is the vector sum of the originally applied magnetic field, typically static, and the RF magnetic field associated with the pulse. The relaxation of the dipoles from their re-aligned position back to the original position when the energy coupling is ended produces signals that can be detected and analyzed to identify components of the sample.
Most NMR analysis to date has been done in large and expensive installations that are typically sized to admit a human subject into the region of controlled magnetic fields. Such installations are usually sufficiently complicated to require an operator or operators when the installations are functioning. The result is a large and expensive piece of equipment that is appropriate only for use in a research laboratory or a hospital, and not in a factory or industrial kitchen.
The production of certain foodstuffs would be aided by the ability to use NMR analysis in a pipeline or other such conduit to measure characteristics of flowing liquids, pastes, slurries or solids in powdered or other finely divided form. Continuous or continual analysis of butterfat or cholesterol content would be useful in manufacturing and quality control of dairy products. Fluids containing fats or oils could be analyzed to control processes for manufacturing margarine and similar substances. Doughs and other pasty materials which may be difficult to analyze continuously by other means could be analyzed in-line. These and other such uses, however, require an NMR machine that is suitable for installation and operation in a factory environment and that needs no more than routine operator attention. Such an NMR machine would need one or more surface excitation and pickup coils that are exposed to the flow of material that is to be analyzed, and it would need a flow rate in a sampling area that was related to the relaxation time of the component being tested.
The present invention overcomes the disadvantages of the prior art by providing analysis of flowing streams of liquids by nuclear magnetic resonance with an apparatus that is small enough, economical enough and simple enough to operate so that it is useful for making measurements in applications such as the production of fruits and the like.
Where the flowable material is in a main conduit of a first diameter, a sampling conduct of a second smaller diameter is associated with the main conduit for selectively receiving the flowable material to be analyzed. An NMR device is coupled to the sampling conduit for subjecting the flowable material to the necessary magnetic fields to generate NMR signals and to receive the generated NMR signals for analyzing the flowable materials. A first selectively closable valve is placed in the main conduit for diverting the flowable material to the sampling conduit. If desired, at least one selectively closable valve is placed in the sampling conduit on one side of the coupled NMR device to allow the diverted material to enter the portion of the sampling conduit in the fixed magnetic field for analysis by the NMR device. In one embodiment, the NMR sampling coil is simply wrapped around the sampling conduit for providing the NMR analysis. In another embodiment, the sampling conduit is mounted within the main conduit for receiving a flowable material. The sampling conduit is mounted in the main conduit in a fixed magnetic field such that at least a portion of the sampling conduit is within the magnetic field. The sampling conduit is mounted in the main conduit with a non-metallic, non-magnetic base member coupling the main conduit and the sampling conduit for holding the sampling conduit centered within and parallel to the main conduit. The base member is elongated in the direction of material flow and has a shape such as an ovate cross-section to reduce resistance to the material flow in the main conduit. A coil encircles the flowable material in the sampling conduit with its elongated axis parallel to the direction of the material flow so as to cause a concentrated magnetic field in the flowable material within the sampling conduit. Electrical conductors are embedded in the base and couple the coil to the NMR device for enabling the flowable material to be subjected to the NMR pulse energy and for coupling the generated NMR signals to the NMR device.
In another embodiment, the coil is mounted in the sampling conduit with its elongated axis perpendicular to the material flow. A non-metallic, non-magnetic elongated support for the coil allows the flowable material in the sampling conduit to be sufficiently close to one side of the coil to be excited by the RF pulsed energy and sufficiently far from the other side of the coil to be substantially unaffected by the RF pulsed energy so as to minimize the generation of NMR signals of opposite phase. The mounting device for the coil comprises a non-magnetic, non-metallic elongated support for the coil extending perpendicular to the longitudinal axis of the sampling tube for supporting the coil adjacent to the flow of material in the sampling tube. A non-metallic, non-magnetic base is attached to the support and the sampling conduit such that the material flows sufficiently close to only one side of the coil on the elongated support to be excited by the RF pulsed energy and on each side of the base sufficiently far from the coil to be substantially unaffected by the RF pulsed energy. Thus the base is in the general shape of a T having arcuate surfaces connecting each end of the horizontal arm of the T to the base of the T, the horizontal portion of the T being attached to the elongated support and the base of the T being attached to the sampling conduit. Both the elongated support and the base have a shape, such as an ovate cross-section, to reduce resistance to material flow in the sampling conduit.
In another embodiment, the sampling conduit of a second smaller diameter is associated with the main conduit of a larger diameter for selectively receiving the material. A test conduit is rotatably coupled to the sampling conduit for receiving the material. An NMR device is coupled to the test conduit for subjecting the flowable material therein to a fixed and a variable magnetic field to generate NMR signals and receive the NMR signals for analysis of the flowable material. The test conduit is rotatable with the material flowing therein during subjection of the material to the fixed and variable magnetic fields to correct for irregularities in the magnetic fields.
Thus, it is an object of the present invention to provide an apparatus for performing NMR analysis on flowing materials.
It is a further object of the present invention to provide an apparatus for measurement of characteristics of flowing materials in a factory environment using NMR.
It is yet another object of the present invention to provide an apparatus for making NMR measurements on liquids that are flowing in a conduit.
It is still another object of the present invention to provide an apparatus for NMR measurements on divided solid materials that are flowing in a conduit.
It is also an object of the present invention to provide an apparatus for continual sampling of materials from a flowing stream of materials in a conduit and testing properties of those materials by NMR analysis.
Other objects will become apparent in the course of a detailed description of the invention.